The best view for assessing the airworthiness of the wing is marked by an innocuous looking black triangle

Retired aerospace engineer Lee Ballentine wrote on website Quora: "The black triangle marks the location of what has been called the ‘William Shatner Seat’, or the seat with the clearest view of the wing.

"The Shatner reference is to one of the strangest Twilight Zone episodes, 'Nightmare at 20,000 Feet'. In it, Shatner’s character sees a gremlin on the wing of the plane he’s a passenger on."

The emergency toilet latch

In the event of an emergency, cabin crew can access occupied toilets by using a small button.

Underneath the lavatory sign will be a catch that, once turned, will turn the lockCredit: Sándor Tarnóczi/ YouTube

Handcuffs, defibrillators and handguns

If unruly passengers overstep the mark, they could find themselves in cuffs and being handed over to airport police.

These aren't the typical metal handcuffs though - it’s far more likely that cabin crews are issued with cable ties as restraining tools.

Meanwhile, since 9/11, sky marshals on flights to and from the US have been allowed to carry concealed weapons on planes - they function as undercover armed escorts, ready to leap into action should the need arise.

Just who is “packing heat” is kept a secret from even the cabin crew though.

In August 2018, a United Airlines steward caught a glimpse of a marshal’s gun, which caused an emergency landing — with the marshal arrested, mistaken for a rogue passenger with a gun.

A defibrillator is also found on most aircraft, to be used if any passenger suffers a cardiac arrest.

The bleed hole

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The hole you see is only there to take pressure off the inner pane of glassCredit: Alamy

It wouldn’t be space or weight-efficient to provide every passenger with an aqualung. Instead, there is a mixture of barium peroxide, sodium chlorate and potassium chlorate — powders and liquids that react violently together to rapidly produce oxygen.

The secret bedroom

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Most long-haul aircraft are designed with crew compartments for attendants to nap and take a breakCredit: Getty - Contributor

Have you ever wondered where the crew go to get away from the passengers?